I will have to update this more later, Ive just wanted to do this one for a long time
From time to time you get people that don’t understand what a pre cat is or where its located. so below is the Pre Cat & main cat description in picture form.
http://audirevolution.net/addons/albums/images/887532777.jpg
Ill start with what the cat looks like on a B6 S4 Stock. This is a picture of the Pre cat (stock)
http://audirevolution.net/addons/albums/images/166578333.jpg
The stock cat is hard to beat. The stock cat is massively expensive and there super strong.
What happens when you get cheap aftermarket Dp’s? where they tell you how great there cats are?
http://audirevolution.net/addons/albums/images/552087760.jpg
Most of the time when profit is the end goal for some of these so called performance companys and the theme isn’t what top grade parts can they supply but, what cheap china knock offs can they sell and hope they don’t fail till long after the customers money is spent
http://audirevolution.net/addons/albums/images/35867575.jpg
its horrendous, You would have been better just keeping the stock cat in at that point in time.
Even after moderate usage the aftermarket Pre Cats get damaged. The stock Pre Cat is 50x better and stronger then the aftermarket cats. You can see even though this aftermarket cat isn’t completely failed its on its way out. You can see its starting to fall apart.
http://audirevolution.net/addons/albums/images/433518584.jpg
You can see the cat is dirty, as Aftermarket cats don’t actually do what there meant to do in most cases. What gets me is people pay extra for high flow cats and in most cases the high flow cats won’t keep the CEL off because they flow too much to help pass emissions, but not enough to justify them being there.
Lets look at the stock 50+K mile cat. again Vs. the 10k mile Aftermarket cat above
http://audirevolution.net/addons/albums/images/166578333.jpg
Obviously you can see the aftermarket cat looks like it will flow better, and it will, but its still failing and a failed cat is worse then a stock cat. The Pre cat is bad for performance, if its a stock or a high flow. With piggies your removing the Pre Cat on the piggie pipes so its not even an issue.
To further drive home the point on why the piggie pipe Dp’s are better then the aftermarket Dp’s with the pre cats. Look how big the surface area is for the main cat. The area opens to twice that of the stock and aftermarket Pre cats.
With such a large area in the main cat lead in, and the fact that the main cat flows better then the pre cat (stock) the flow threw the main cat isn’t restricted as much and there is actually more performance in keeping the main cat over using a High flow pre cat.
http://audirevolution.net/addons/albums/images/596453446.jpg
all the above and the fact that power wise, the main cat is located far enough away from the motor to allow proper undisturbed flow. This makes for a big beit of piggies over the aftermarket Dp’s with the Pre cats.
If you had to chose between Stock Piggie DP’s and aftermarket Pre Cat Dp’s I say go piggies.
If you can go cat less then go cat less 2.5 if you can go all out go headers as there 10x better then all options.
As headers actually take out the need for Dp’s and they replace the stock exhaust manifold. More on that in another post.
more Precome.
;D